18.1 The Electromagnetic Spectrum The energy field created by electricity and magnetism can oscillate and it supports waves that move. These waves are called electromagnetic waves.

18.1 The Electromagnetic Spectrum Electromagnetic waves have both an electric part and a magnetic part and the two parts exchange energy back and forth. A 3-D view of an electromagnetic wave shows the electric and magnetic portions. The wavelength and amplitude of the waves are labeled λ and A, respectively.

18.1 The Electromagnetic Spectrum The higher the frequency of the light, the higher the energy of the wave. Since color is related to energy, there is also a direct relation between color, frequency, and wavelength.

18.1 Speed of Light c = f  Wavelength (m) Speed of light 3 x 108 m/sec c = f  Frequency (Hz)

18.1 Waves of the electromagnetic spectrum Visible light is a small part of the energy range of electromagnetic waves. The whole range is called the electromagnetic spectrum and visible light is in the middle of it.

16.1 Electric Light The process of making light with heat is called incandescence. Incandescent bulbs generate light when electricity passes through a thin piece of metal wire called a filament. The filament heats up and gives off light.

16.1 Electric Light The other common kind of electric light is the fluorescent bulb. Fluorescent bulbs convert electricity directly to light without generating a lot of heat. Fluorescent bulbs use high-voltage electricity to energize atoms of gas that fill the bulb.

16.1 Light intensity The intensity of light from a small source follows an inverse square law because its intensity diminishes as the square of the distance.

16.1 The speed of light The speed at which light travels through air is approximately 300 million meters per second. Light travels almost a million times faster than sound.

16.2 Color and Vision When all the colors of the rainbow are combined, we do not see any particular color. We see light without any color. We call this combination of all the colors of light "white light".

How the human eye sees color The retina in the back of the eye contains photoreceptors. These receptors release chemical signals. Chemical signals travel to the brain along the optic nerve. optic nerve

Photoreceptors in the eye Cones respond to three colors: red, green and blue. Rods detect intensity of light: black, white, shades of gray.

How we see colors Which chemical signal gets sent depends on how much energy the light has. If the brain gets a signal from ONLY green cones, we see green.

16.2 How we see other colors The three color receptors in the eye allow us to see millions of different colors. The additive primary colors are red, green, and blue. We don’t see everything white because the strength of the signal matters. All the different shades of color we can see are made by changing the proportions of red, green, and blue.

16.2 How does a color TV work? Televisions give off light. To make color with a TV, you can use red, green, and blue (RGB) directly. The screen is made of tiny red, green, and blue dots. The dots are called pixels and each pixel gives off its own light. TV sets can mix the three colors to get millions of different colors.